Dominant mechanisms in the reduced localized corrosion resistance of carbon steel weldments were investigated with the aid of experimental sulfur-rich (0.1 wt percent S) and low-sulfur (0.01 wt percent S) carbon steels, exposed to 3.5 percent sodium chloride (NaCl). Experimental techniques included mapping current density in the solution above corroding samples (by using a scanning vibrating electrode), zero-resistance ammetry, exposure of autogenously welded samples to flowing solution, and examination of microstructure by optical and scanning electron microscopy. It was found that galvanic corrosion between different microstructures in the weldment is probably not the main cause for the localized attack, and it is proposed that, for the conditions investigated, grooving is caused primarily by the unique combination of active sulfides and networks of small sulfides on original austenite grain boundaries in the fusion line area.
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